Many have considered it desirable to build engines running at higher temperatures. Efficiency would improve, since it is dependent on the difference in temperature between ambient air (which is constant) and that at combustion. The resulting hotter exhaust gases will generally be easier to cleanse. If the cooling system can be eliminated, so can its cost, mass, bulk and unreliability. Uncooled engines can be thermally, acoustically and vibrationally insulated to virtually any degree, making them more environmentally and socially acceptable. Of the calorific value of the fuel, a greater amount will be spent on pushing a piston, but nearly all the remainder will now be in the hot exhaust gas, where it is recoverable. With the new engines, temperature equilibria would be so high that the main piston and cylinder components would likely have to be of ceramic material.
To the knowledge of the applicant, un-cooled engines are not in production today. Manufacturers and researchers tried to build un-cooled engines in the 1980's and earlier. Publications indicate the work nearly all involved substituting ceramic materials for metals in key combustion chamber components. For example, ceramic caps were placed on metal pistons; ceramic liners placed in metal engine blocks; a zirconia poppet valve was substituted for an identically shaped metal valve. The work was not very successful for a number of reasons, including problems with differential thermal expansion of ceramic and metal components abutting each other. Engine designs were essentially unchanged.
Early internal combustion (IC) engine designers like Gottfried Daimler and Rudolf Diesel adapted the mid-18th century metal piston-and-cylinder technology developed for steam engines. Today's metal IC engines reflect three constraints; the materials characteristics of metals; the need for cooling and therefore the engine block, etc; and commercial practice determining the most viable ways of manufacturing and assembling metal components.
The applicant felt that any viable commercial embodiment of the un-cooled ceramic engine would look very different from today's units, because all the old constraints were no longer relevant, and new constraints would apply. This disclosure is the result of his attempt to adapt and modify the traditional design of the piston and cylinder engine, so that new embodiments could be viably built un-cooled and out of ceramic material. Because exhaust emissions control is so important today, new arrangements for cleansing high temperature exhaust gases were devised, and are disclosed herein.
In today's typical engine, roughly one third of the calorific value of the burnt fuel is put to work driving the piston, one third is dissipated via the cooling system and general radiation by the engine components and one third is carried away by the exhaust gases. The latest large diesels for trucks and marine applications have efficiencies in the 40% range, but the average for all engines now operating is close to 30%. Current large engines, as used in ships and electricity generating stations, often have some form of compounding, which entails using a device (say a turbine) to derive further work from the hot exhaust gases.
In un-cooled engines, the combustion process takes place at higher temperatures, leading to efficiency increases of anywhere between 0 and 20%, dependant on design and construction details. A reasonable projection could be 10%, enough to make to make a substantial difference to the oil needs and political situation of a country such as the USA. In compounded un-cooled engines greater efficiencies can be expected, since the exhaust energy conversion devices have a greater portion of the fuel's calorific value to work with—somewhere between 50 and 60% could be in the hot exhaust gas. Turbines or steam engines may be used to extract work from the hot gas; optionally the gas heat can be converted into electrical energy. At their present stage of development, heat to electrical energy devices have very approximately 25% efficiency.
The un-cooled engine preferably uses the internal combustion cycles, although the principles of the invention may also be applied to, for example, engines operating on the Rankine or Stirling cycles. It is intended to construct such an engine to operate continuously in an un-cooled state, so that it might be used to power, for example, generating plant, light cars and trucks, heavy goods vehicles, locomotives, marine vessels including supertankers, etc. Heat can be extracted from the area of, or downstream of, an exhaust gas reactor to provide further work. The invention may be used in association with a means of converting the flow of exhaust gas into mechanical energy.